(Health.com) -- If you have perpetually clogged and swollen sinuses, secondhand smoke -- even in small amounts may be to blame. According to a new study, secondhand smoke may be responsible for up to 40 percent of cases of chronic sinusitis.

"People should be aware of their exposure when they go to friends' houses, when they go to parties and weddings, [when they're] playing card games," says the lead author of the study, Martin Tammemagi, Ph.D., an associate professor of community health sciences at Brock University, in St. Catharines, Ontario. "They shouldn't allow themselves to be exposed and they shouldn't be exposing other people."

Sinusitis describes a range of unpleasant and sometimes debilitating symptoms that include nasal and sinus inflammation, congestion, cough, runny nose, difficulty breathing, and a reduced sense of smell. The chronic version of the condition -- which is defined as lasting for 12 weeks or more -- affects about 1 in 6 adults in the U.S., according to the study.

In the study, Tammemagi and his colleagues surveyed more than 600 nonsmokers from the Detroit area -- half of whom had been diagnosed with chronic sinusitis -- about their exposure to secondhand smoke at home, at work, in public places (such as bars, restaurants, and bowling alleys), and in private social settings over a five-year period.

In each case, more people diagnosed with sinusitis reported being exposed to secondhand smoke. More than 50 percent of those with sinusitis said they'd inhaled secondhand smoke at private parties and social functions, compared with just 28 percent of those who did not have sinusitis, for instance.

Overall, the researchers found, breathing secondhand smoke in private social settings nearly tripled the risk of being diagnosed with sinusitis, while breathing it at work more than doubled the risk. Being exposed to secondhand smoke at home or in public places increased the risk of diagnosis by 69 percent and 50 percent, respectively, according to the study. (To pinpoint the effects of secondhand smoke, the researchers factored in the participants' socioeconomic status and their exposure to air pollution and other airborne irritants.)

And the more often people inhaled cigarette smoke, the more likely they were to develop sinusitis. "The dose was fairly directly related to the amount of chronic sinusitis that people developed," says David Arnold, M.D., a professor of otolaryngology at the University of Miami Miller School of Medicine.

The study has important implications for public health, adds Arnold, who was not involved in the research. "If 40 percent of chronic rhinosinusitis is caused by secondhand smoke, you're in a good position to eliminate...those cases if you eliminate secondhand smoke," he says.

The study appears in the April issue of Archives of Otolaryngology--Head & Neck Surgery.

Secondhand smoke can increase the risk of respiratory ailments, lung cancer, and heart disease in nonsmokers, and the risk of sudden infant death syndrome and middle ear infections in children. Despite the spread of antismoking laws, 60 percent of nonsmokers in the U.S. are still exposed to the toxic chemicals in cigarette smoke, according to the study.

Although the link between sinusitis and secondhand smoke might seem obvious, few studies have examined it. "Scientifically, [the finding] is not surprising, but I'm not aware of such a carefully done study," says Norman Edelman, M.D.the chief medical officer of the American Lung Association. "The results are pretty convincing."

"We know that secondhand smoke contains thousands of irritating chemicals, and [we] suspect that they damage the immune system and lead to invasion by infectious agents," says Tammemagi. "Also, the irritants in the secondhand smoke can lead to changes in the permeability of the membranes lining the nose and sinuses. This could make it more possible for allergens and toxins to enter the cells of the tissue."

Perhaps because it is so common, chronic sinusitis is often dismissed as a nuisance, says Edelman. "It's not fun at all," he says. "People tend to shrug it off the way they shrug off asthma, but it's a serious problem."

The study's bottom line is simple -- and it's one that people have heard before, says Jordan Josephson, M.D., a sinus and nasal specialist at Lenox Hill Hospital, in New York City, and the author of Sinus Relief Now.

"People really need to stop smoking and stop being around secondhand smoke," he says.